1. Field of the Invention
This invention relates to a structure for mounting a sensing element for measuring the load of a vehicle into a trunnion shaft which is used to support the suspension of a vehicle such as a truck and the like.
2. Background
The measurement of a load of a vehicle is performed mainly on a large-size vehicle such as a truck and, for example, for the purposes of preventing traffic accidents such as turnover due to overload, and for preventing deterioration of the vehicle and surfaces of the road from being stimulated.
Conventionally, the vehicle load measurement is carried out by placing a vehicle to be measured on a platform scale which is so called "KANKAN" in Japanese. However, since such conventional load measurement requires a facility which has a large-scale and wide installation space, the number of platform scales that can be installed is limited to thereby be unable to measure the loads of many vehicles, and further, the installation costs are high.
In order to avoid the above-mentioned inconveniences, in recent years, there has been supplied a load measuring device which can be carried on a vehicle itself for measurement of the load of the vehicle.
As the above-mentioned conventional load measurement device of an on-board type, for example, as disclosed in Japanese Utility Model Publication No. Hei. 6-69759, there is known a load measurement device structured such that a plurality of sensing elements for load measurement such as a gauge sensor of a torsion type or the like are mounted within trunnion shafts which are respectively disposed in the neighborhood of the two end portions of the axle of a vehicle and are used to support the suspension of the vehicle, and the load of the vehicle is calculated in accordance with the sum of the measured values of all the sensing elements.
Now, description will be given below of the structure of the load measurement device disclosed in the above-mentioned Japanese Utility Model Publication No. Hei. 6-69759 with reference to FIGS. 5 to 7.
FIG. 5 is a perspective view of the trunnion shaft portion of a vehicle the load of which is to be measured by the load measurement device. In FIG. 5, reference character 37 designates a trunnion shaft, while 36 stands for a trunnion bracket on which the trunnion shaft 37 is to be mounted.
The trunnion bracket 36 includes a flat-plate-shaped flange 36a, and a support portion 36b which is projected from one surface of the flange 36a.
In the support portion 36b, there is formed a through hole 36c extending in parallel to the flange 36a and also, in the portion of the support portion 36b that is situated slightly nearer to the flange portion 36a than the through hole 36c, there is formed a pin hole 36d which extends through the present portion at right angles to the through hole 36c and in parallel to the flange 36a. The pin hole 36d is, within the support portion 36b, in communication with the through hole 36c.
The flange 36a is mounted on and fixed to a load-carrying platform frame 33 of the vehicle by bolts and nuts (not shown) in the following manner: that is, the trunnion bracket 36 faces in such a manner that the through hole 36c extends along the vehicle width direction A of the vehicle and the pin hole 36d extends in the longitudinal direction B of the vehicle, while the opposite surface of the flange 36a to the surface thereof from which the support portion 36b is projected abuts against the lower surface of the load-carrying platform frame 33.
The trunnion shaft 37 is formed in a cylindrical shape which has an outside diameter corresponding to the inside diameter of the through hole 36c and has a length sufficiently larger than the axial dimension of the through hole 36c. Also, the trunnion shaft 37 includes an annular flange 37a which is provided on and projected from the outer peripheral surface of the trunnion shaft 37 in the axially, substantially central portion of the trunnion shaft 37.
Further, in the trunnion shaft 37, a suspension support portion 37b is formed by the trunnion shaft 37 portion that is situated on one end 37A side of the flange portion 37a, while an insertion portion 37c corresponding in length to the through hole 36c is formed by the trunnion shaft 37 portion that is situated on the other end 37B side of the flange 37a.
The above-mentioned insertion portion 37c is structured in the following manner: that is, the insertion portion 37c is inserted into the through hole 36c of the trunnion bracket 36 from outside in the vehicle width direction A toward the central side of the through hole 36c until it abuts against the support portion 36b position in the peripheral edge of the through hole 36c, thereby positioning the one end 37A of the trunnion shaft 37 on the outside in the vehicle width direction A, and positioning the other end 37B on the central side in the vehicle width direction A; and, in this state, at a position where the through hole 36c and pin hole 36d are in communication with each other, as shown by a section in FIG. 7, a fixing bolt 38 inserted into the pin hole 36d can be engaged with a recessed groove 37d having a substantially semicircular section which is formed in the outer peripheral surface of the insertion portion 37c and in the outer peripheral surface portion thereof nearer to the other end 37B of the trunnion shaft 37.
Also, on the above-mentioned suspension support portion 37b, there is mounted an annular spring support member 35 used to support a leaf spring 34 which, with grease applied thereto, can function as the suspension of the vehicle. And, in the portion that extends from one end 37A of the trunnion shaft 37 to the end face of the spring support member 35, in particular, to the position thereof corresponding to the end face portion of the peripheral edge of one end 37A of the trunnion shaft 37, there is removably mounted a cap 37e in order to prevent the grease from leaking out externally from the boundary portion between the outer peripheral surface of the suspension support portion 37b and the inner peripheral surface of the spring support member 35.
Here, description will be given below of a sensing element for vehicle load measurement which is disposed in the interior of the above-structured trunnion shaft 37, with reference to a perspective view thereof shown in FIG. 6.
In FIG. 6, reference character 7 designates a sensing element, while the present sensing element includes a plate-shaped member 7a and a coil 7g.
The plate-shaped member 7a is formed of magnetic material such as permalloy or the like in a flat shape having a substantially rectangular plan view, while the plate-shaped member 7a includes a coil portion 7b formed in the substantially central portion of the plate-shaped member 7a in the longitudinal direction thereof, and two fixing portions 7c, 7c respectively formed on the two sides of the coil portion 7b.
In a total of four edge positions which are respectively situated in the two edge portions of the plate-shaped member 7a in the width direction thereof extending at right angles to the above-mentioned longitudinal direction and in the boundary portions between the coil portion 7b and two fixing portions 7c and 7c, there are formed four substantially semicircular notches 7e which are respectively used to relieve stresses acting on the plate-shaped member 7a. Also, in the coil portion 7b which is defined inside the four notches 7e, there are formed four through holes 7f which respectively extend through the coil portion 7b in the above-mentioned longitudinal and width directions at intervals.
The coil 7g includes two magnet wires 7h which form a cross coil, while these magnet wires 7h are respectively covered with insulation material (not shown) such as enamel or the like.
One of the two magnet wires 7h is wound over the two through holes 7f and 7f which are disposed opposed to each other in the above-mentioned longitudinal direction, while the two ends of the magnet wire are respectively drawn out from the through holes 7f and 7f. Also, the other magnet wire 7h is wound over the remaining two through holes 7f and 7f which are-disposed opposed to each other in the above-mentioned width direction, while the two ends of the magnet wire are respectively drawn out from the through holes 7f and 7f. Further, the two magnet wires 7h are covered with insulation cover films such as vinyl or the like to thereby provide a lead wire 7j.
Now, in the sensing element 7, if current flows one of between the two ends of the magnet wire 7h wound over the two through holes 7f and 7f which are disposed opposed to each other in the longitudinal direction of the plate-shaped member 7a and between the two ends of the magnet 7h wound over the remaining two through holes 7f and 7f which are disposed opposed to each other in the width direction of the plate-shaped member 7a, then there is generated a magnetic field in the plate-shaped member 7a and an induced current is thereby caused to flow between the two ends of the other magnet wire 7h.
In this state, if a load is applied onto the plate-shaped member 7a and the plate-shaped member 7a is thereby distorted along the width direction thereof, then the magnetic field of the plate-shaped member 7a is caused to vary in direction, so that the induced current flowing between the two ends of the other magnet wire 7h is caused to vary.
As a result of this, the current that corresponds in intensity to the load applied onto the plate-shaped member 7a can be obtained from the two ends of the other magnet wire 7h as the output thereof.
By the way, in FIG. 6, reference character 7A designates a sensor main body which has the sensing element 7 portions except for the lead wire 7j.
When the thus structured sensing element 7 is arranged in the interior portion of the trunnion shaft 37, conventionally, there has been employed such a structure as follows, because an amplifier (not shown) used to amplify the output signal of the sensing element 7 is disposed in the bottom portion of the vehicle body situated substantially centrally in the vehicle width direction A.
That is, as shown in FIG. 7, for easy arrangement or connection of the lead wire 7j with respect to the amplifier, in a state that the lead 7j is inserted into the through hole 36c of the trunnion bracket 36, in the other end 37B of the trunnion shaft 37 situated in the center side of the vehicle in the vehicle width direction A, an insertion hole 37f extending along the axial direction of the trunnion shaft 37 toward the one end 37A side thereof is opened up in such a dimension that the depth of the insertion hole 37f in the axial direction of the trunnion shaft 37 reaches the provision position of the flange 37a, the plate-shaped member 7a, with the lead wire 7j remaining left outside the insertion hole 37f, is inserted into and stored in the deep portion of the insertion hole 37f in such a posture that the width direction of the plate-shaped member 7a extends in the height direction of the vehicle, the cap 38 having a through hole 39a formed in the central portion thereof is threadedly engaged with an internal thread 37g formed in the inner peripheral surface portion of the neighborhood of the entrance of the insertion hole 37f, and the lead wire 7j drawn out externally of the insertion hole 37f from the through hole 39a is connected to the above-mentioned amplifier (not shown).
And, the fixation of the plate-shaped member 7a within the insertion hole 37f is achieved in the following manner: that is, the inside diameter of the insertion hole 37f is set equal to or slightly smaller than the dimension of the plate-shaped member 7a in the width direction thereof, and the plate-shaped member 7a is pressed into the insertion hole 37f.
However, in the mounting structure of the above-mentioned conventional sensing element 7, due to the fact, for easy arrangement of the lead wire 7j, the plate-shaped member 7a is inserted into the insertion hole 37f from the other end 37B of the trunnion shaft 37 situated on the central side of the vehicle, an operator must crawl under the lower side of the vehicle to carry out the insertion operation.
Also, since the plate-shaped member 7a of the sensing element 7 is pressed into and fixed to the insertion hole 37f of the trunnion shaft 37, when the magnet wires 7h or lead wire 7j are out of order, for example, when they are cut, the plate-shaped member 7a cannot be removed from the trunnion shaft 37 due to its fixation to the deep portion of the insertion hole 37f, so that the sensing element 7 cannot be removed individually but it must be removed together with the trunnion shaft 37 for maintenance.